Many computing devices display digital maps that assist users in navigation. A digital map can be a digital representation of a portion or region of the world and may include representations of roads, rivers, bridges, buildings, parks, and other physical objects. Individual roads may be described by road data that includes a list of two-dimensional (2D) points (e.g., x and y coordinates, polar coordinates, etc.) or three-dimensional (3D) points (e.g., x, y, z coordinates, where the z coordinate is incorporated to represent height/altitude). A digital map can be broken up into one or more map tiles that each correspond to a region that is presented by the digital map. When a user computing device zooms into a region of the digital map, the one or more tiles presented by the computing device may be divided into a subset of tiles that each correspond to the portion of the region into which the user has zoomed.
Digital maps are often rendered with visual representations of the traffic conditions associated with roadways presented within the digital maps. For example, the GPU of a user computing device may render a portion of road as being a particular color (e.g., green/yellow/red/black) to indicate the traffic condition (e.g., normal/slow/bad/motionless) of the portion of road. In some instances, GPU may render multiple representations of traffic for a single portion of road, with individual representations indicating the traffic conditions of the portion of road in a particular direction, lane, etc. For example, where northbound traffic on a portion of road is slower than a posted speed or average speed, the user computing device may render the northbound side of the corresponding portion of road as a yellow line or a red line. Additionally, if the southbound traffic on a portion of road is normal (e.g., at or near a posted speed or average speed, etc.), the user computing device can render the southbound side of the corresponding portion of road as a green line.
In order to enable computing devices to present current traffic conditions, digital map service providers analyze traffic message channel codes, which are an industry standard for providing current traffic conditions, and transmit the traffic conditions to the computing device. The digital map server can receive traffic information (e.g., traffic message channel (TMC) codes, etc.) that corresponds to one or more roads from one or more sources that gather world traffic data. In some instances, the traffic information may be collected and/or accessed from one or more sources, including GPS data, speed detectors, sensors, etc. The digital map server can then determine traffic conditions for a portion of a road by comparing the traffic information with expected traffic speeds for the portion of the road. For example, for a portion of road that has a speed limit of 60 mph, when the TMC codes indicate that traffic is traveling at 60 mph, the digital map server can then determine that the traffic condition for the portion of road is normal. Alternatively, if the TMC codes report that traffic is moving at 0 mph, the digital map server may determine that the traffic condition for the portion of road is at a standstill.
Additionally, as many computing devices receive the traffic conditions via communications where bandwidth is limited, it is desirable for the current traffic conditions to be transmitted as efficiently as possible. Moreover, as a digital map presented by a computing device may include many different roads, and since each road may be associated with multiple different traffic conditions, it is also desirable for the traffic conditions to be transmitted in a way that allows large quantities of traffic information to be transmitted in as few transmissions as possible.